Wrapping, in sealed fashion, industrial goods, daily needs, provisions and other items with the use of the property of shrinking, when heated, of a biaxially oriented film of thermoplastic resin, generally known as shrink wrapping, is now widely performed. For example, low density polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride and polyesters are commonly used as materials of the above film for shrink wrapping. However, all the films prepared from these materials do not necessarily exhibit highly satisfactory performance as shrink wrapping films.
For example, a film of low density polyethylene is available at low cost and has high impact strength, so that it is suitable for industrial wrapping. However, the transparency and gloss thereof are not so good and the film has an optimum shrink temperature being 20 to 50.degree. C. higher than that of a soft vinyl chloride film (hereinafter referred to as "PVC film"). Further, the surface hardness thereof is so low that, when goods are piled one upon another, the low density polyethylene film is likely to have flaw and the appearance of wrapped goods is likely to be deteriorated. Therefore, the low density polyethylene film is not suitable for commercial wrapping. On the other hand, the PVC film has such an excellent transparency that the beauty of wrapped goods is enhanced to thereby increase the value thereof. Further, the PVC film has an optimum shrink temperature which is low and broad. Therefore, the performance of the PVC film is one most suited for commercial wrapping. However, the PVC film cannot be used in industrial wrapping because its impact strength, especially, impact strength at low temperature is poor.
Moreover, this film involves various problems such as a problem of food hygiene attributed to a plasticizer contained in the film, a migration of the plasticizer to the wrapped goods, a tendency for film blocking and a difficulty in disposal of the film after use. Thus, substituting polyolefin films therefor is now being studied. Although the polyolefin films are characterized by having high transparency and gloss, possessing nerve and exhibiting high shrinkage stress, they have drawbacks in that their impact strength is low and their optimum shrink temperature is high and narrow. Therefore, a method of lowering the optimum shrink temperature by copolymerizing propylene with a small amount of ethylene has been proposed. However, when the ethylene content is increased, the propylene/ethylene copolymer films tend to stick to each other to thereby suffer from blocking. Further, ethylene is heterogeneously incorporated in the polymer, so that there occur problems such that the transparency of the film is deteriorated. Therefore, the ethylene content of the propylene/ethylene copolymer which can be used in shrink wrapping is generally limited to a maximum of 10 mol %. Although significantly lower than that of a polypropylene film, the optimum shrink temperature of the propylene/ethylene copolymer film with the above ethylene content is still about 20 to 50.degree. C. higher than that of a polyethylene film.